Conventionally, industrial robots have been developed that include a plurality of links rotatably connected to each other and are configured to cause an actuator to rotationally drive the links to perform a predetermined operation using an end effector (for example, a torch for arc welding) attached to an end of one of the links (see Japanese Patent Application Laid-open No. 2008-73775, for example).
In the technique disclosed in Japanese Patent Application Laid-open No. 2008-73775, a robot includes an external gear connected to an actuator and an external gear connected to a link and is configured to engage the two external gears with each other to transfer the drive force of the actuator to the link, causing the link to perform rotational drive.
However, the configuration described above is associated with a concern that the connection part between the actuator and the link in the robot will be enlarged in the direction perpendicular to the rotation axis of the gears, in other words, in the radial direction of the gears. More specifically, when the two external gears are engaged with each other, there is a concern that the connection part between the actuator and the link will be enlarged because the entire width of the gears in the radial direction is approximately the value obtained by adding the outer diameter of one external gear with that of the other external gear.
If the entire body of a robot is large due to a large connection part between an actuator and a link as described above, the robot may interfere with a workpiece, for example, in performing a predetermined operation. Reduction in the size of connection parts has been therefore desired.